1. Field of the Invention
The present invention relates to an IP (Internet Protocol) conference telephone system and more particularly to an IP conference telephone system advantageously applicable to, e.g., a private branch exchange (PBX) system.
2. Description of the Background Art
A conference telephone service is not available with the state-of-the-art IP-PBX system that assembles a voice signal into an IP packet and connects it by switching. A conventional digital PBX system includes a time-division switch accommodating a highway to which a conference trunk or bridge is connected. Voice signals are sent from telephone subscriber sets accommodated in a subscriber circuit to the time-division switch by being multiplexed on the preselected channels of the highway. The switch switches the voice signals to the conference trunk. The conference trunk adds all the voice signals on the channels of the telephones to be connected for a session except for a voice signal on the channel assigned to a particular telephone. The conference trunk then returns the resulting sum signal to the switch as a signal on the channel of the above particular telephone subscriber set.
Today, the IP-PBX system can be readily implemented with the spreading Intranet practicable with, e.g., a LAN (Local Area Network). Therefore, a conference telephone service available with the digital PBX should preferably be realized with the IP-PBX system also.
It is therefore an object of the present invention to provide an IP conference telephone system particularly feasible for an IP-PBX system.
In accordance with the present invention, an IP conference telephone system includes a network for transferring IP packets. A plurality of telephone terminal systems include telephone terminals and are accommodated in the network. The telephone terminal systems convert packets received via the network to voice signals and send the voice signals to the telephone terminal, while converting voice signals received from the telephone terminals to packets and sending them to the network. A communication control is connected to the network and sets up, in response to a conference connection request received from any one of the telephone terminal systems, a conference connection to at least three telephone terminal systems relating to the conference connection request. A highway transfers voice signals multiplexed on channels thereof. An IP bridge is connected to the network and highway for multiplexing voice signals of packets received via the network and converting voice signals received over the highway and multiplexed on the channels to packets to thereby send the packets to the network. A conference trunk is interconnected to the highway for performing, upon receiving packets from the at least three telephone terminal systems, addition and subtraction with the voice signals of the packets and returning the results of addition and subtraction to the highway. The at least three telephone terminal systems connected for a conference send packets of voice signals received from the telephone terminals to the network to address them to the conference trunk. This allows a conference to be held between the at least three telephone terminal systems.
A multicast router may be substituted for the above conference trunk for managing a multicast group including the at least three telephone terminal systems in accordance with a multicast address. In such a case, the at least three telephone terminal systems each assign the multicast address to a packet of a voice signal output from the respective telephone terminal and send the packet to the network. Upon receiving the packet with the multicast address from any one of the at least three telephone terminal systems, the network transfers the packet to the other telephone terminals.